Ferromagnetic storage cores and process of making the same

ABSTRACT

Ferromagnetic storage cores and a process of making the same wherein the cores are composed of 3.5 to 15 mol percent of ZnO, 10 to 16 mol percent of LiO2 and 70 to 81 mol percent of Fe2O3 and exhibit a rectangular hysteresis loop with a Rs of more than 0.7 over a broad operating temperature range without current readjustment. The process comprises presintering the core material in a nitrogen atmosphere, then initially sintering in an oxygen atmosphere, continuing sintering in the oxygen atmosphere at an elevated temperature, initially cooling the sintered materials and finally cooling the materials to ambient temperatures.

United States Patent Schmid [5 4] FERROMAGNETIC STORAGE CORES AND PROCESS OF MAKING THE SAME [72] Inventor: Rudolf Schmid, Neu-Germering, Germany [73] Assignee: Siemens Aktiengesellschait, Berlin, Germany [22] Filed: Sept. 26, 1968 [21] Appl. No.: 762,907

[30] Foreign Application Priority Data Sept. 26,1967 Germany ..P 16 71 071.7

[52] U.S. Cl ..252/62.6l

[5 l Int. Cl. ..C04b 35/26 [58] Field of Search ..252/62.61, 62.67

[56] References Cited UNITED STATES PATENTS 3,370,01 l 2/1968 Kitagawa et al. ..252/62.6l 3,413,228 11/1968 Esveldt et a1. ..252/62.6l

Primary Examiner-Robert D. Edmonds Attorney-Hill, Sherman, Meroni, Gross & Simpson ABSTRACT Ferromagnetic storage cores and a process of making the same wherein the cores are composed of 3.5 to 15 mol percent of 2:10, 10 to 16 mol percent of U0, and 70 to 81 mol percent of Fe O and exhibit a rectangular hysteresis loop with a R, of more than 0.7 over a broad operating temperature range without current readjustment. The process comprises presintering the core material in a nitrogen atmosphere, then initially sintering in an oxygen atmosphere, continuing sintering in the oxygen atmosphere at an elevated temperature, initially cooling the sintered materials and finally cooling the materials to ambient temperatures.

14 Claims, 2 Drawing Figures 51 Jan. 25, 1972 I FERROMAGNETIC STORAGE CORES AND PROCESS OF MAKING THE SAME The invention relates to ferromagnetic storage cores and more particularly to ferromagnetic lithium-zinc ferrite storage cores and methods of making the same.

British Pat. specification No. 989,389 suggests a lithium zinc ferrite core having a substantially rectangular hysteresis loop, i.e., a rectangularity ratio R, of at least 0.70 and a relatively high Curie temperature. (The rectangularity ratio R, generally defined as the ratio of the induction of -l-l,,,/2 to the maximal induction B This type of ferrite core exhibits, within a specified temperature range, a low temperature dependence for the electrical data on the core. This reference suggests that zinc oxide within the core be present in amounts up to the maximum of 3.4 mol percent.

U.S. Pat. No. 3,038,860 further suggests that lithium-zinc ferrite cores having amounts of zinc oxide in excess of 3.4 mol percent exhibit a smaller rectangularity ratio R,, which is not more than 0.6. As will be appreciated, a core having such low rectangularity ratio cannot be utilized as a storage ring core.

Accordingly, it is an important object of the invention to provide an improved ferromagnetic lithium-zinc ferrite storage core and the method of making the same.

It is a further object of the invention to provide an improved ferromagnetic lithium-zinc ferrite core having a substantially rectangular hysteresis loop useful over a broad operating range without current readjustment.

It is yet a further object of the invention to provide an improved ferromagnetic lithium-zinc ferritecore composed of 3.5 to 15 mol percent of ZnO, 10 to 16 mol percent of U and 70 to 81 mol percent of Fe O having an R greater than 0.7.

Other objects, features and advantages of the invention will become more apparent with the teachings of the principles of the present invention in connection with the disclosure of the preferred embodiments thereof in the specification, claims and drawing, in which:

FIG. 1 is a phase graph illustrating the preferred compositions of the ferromagnetic cores of the invention; and

FIG. 2 is a graphical illustration of the temperature dependence for the various characteristics of ferrite cores composed of a preferred composition in accordance with the principles of the instant invention.

The present invention provides a lithium-zinc ferrite core and a method of producing the same which exhibits a substantially rectangular hysteresis loop and is usable over a broad temperature range, i.e., to 70 C., without current readjustment. This type of ferrite core is especially preferred in rapidly operating data storage devices, since the hysteresis losses which are caused by the frequent switching of the ferrite cores, result in relatively high heat-generation within the fer.- rite-cores.

Surprisingly, and in contrast to the suggestions of the prior art, it has now been discovered that an increase of zinc oxide (ZnO) above 3.5 mol percent in a lithium-zinc ferrite core produces a data storage core having a rectangular hysteresis loop with a R, greater than 0.7. The ferrite cores produced in accordance with the principles of the present invention are well suited for use as storage ring cores having coincident controls. Further, the storage ring cores of the invention have much shorter switching times than known storage ring cores but their Curie temperatures remain very high. Lithium-zinc ferrite cores made in accordance with the principles of the invention are thus usable over a great temperature range without the need to readjust the current.

The lithium-zinc ferrite cores of the invention are data storage cores composed of a sintered mixture of 3.5 to mol percent of zinc oxide (ZnO), 10 to 16 mol percent of lithium oxide (U 0) and 70 to 81 mol percent of iron oxide (Fe O The schematic phase diagram shown at FIG. 1 graphically illustrates the preferred compositions of the lithium-zinc ferrite cores of the invention in the shaded portions. Points A, B and C on the graph represent embodiments of the composition.

Composition A is substantially about 5 mol percent of ZnO, about 15 mol percent of U 0 and about 80 mol percent of F6 0,; Composition B is substantially about 7.7 mol percent of ZnO, about 14.1 mol percent of U 0 and about 78.2 mol percent of Fe O while Composition C is substantially about 12.5 mol percent of ZnO, about 12.5 mol percent of U 0 and about mol percent of mo, Ferrite cores produced from Compositions A, B or C are exceptionally suited for the production of lithium-zinc ferrite cores of the invention since the cores produced therefrom fully and completely meet all of the desired characteristics set forth. However, it will be appreciated useful ferrite cores may also be produced from other compositions falling within the shaded portion of the phase graph illustrated at FIG. 1.

Generally, the ferrite cores of the invention are produced by (a) forming core blanks of a presintered starting mixture consisting essentially of 3.5 to 15 mol percent of ZnO, 10 to 16 mol percent of U 0 and 70 to 81 mol percent of Fe O and subjecting these core blanks to a heated nitrogen atmosphere for a period of time ranging from 10 to 30 minutes at a temperature substantially in the range of 880 to 960 C. (preferably about 920 C.). Then (b) the core blanks are subjected to initial sintering conditions in an oxygen atmosphere for a period of time ranging from about '15 to 60 minutes at a temperature in the range of about 880 to 960 C. and preferably at a temperature of about 920 C. Thereafter, (c) the temperature of the core blanks (in an oxygen atmosphere) is relatively slowly elevated (during a period of time ranging from 10 to 30 minutes) to a final sintering temperature in the range of 1,060" to l,220 C. and the core blanks are sintered under these conditions for a period of time ranging from several minutes to about 60 minutes. Then, (d) the sintered core blanks are initially relatively slowly cooled in an oxygen atmosphere (for a period of time ranging from about 20 to 30 minutes) to a temperature in the range of 880 to 960 C. and preferably to a temperature of about 920 C. The initially cooled sintered blanks are maintained at this temperature for a period of time ranging up to about 60 minutes. Finally, (e) the initially cooled core blanks are then relatively quickly, i.e., within a few minutes, cooled to ambient temperature in an oxygen atmosphere.

In a preferred embodiment of the invention, core blanks composed of a presintering mixture having the molar compositions illustrated at FIG. 1 or the molar compositions indicated for the preferred compositions A, B or C are suitably formed into core blanks having dimensions of d =0.8 mm., d 0.5 mm. and h=0.2 mm. It will be appreciated that the foregoing dimensions are somewhat approximate. These core blanks are placed in a sintering furnace containing a nitrogen atmosphere and heated to a temperature of about 920 C. for about 10 minutes. Then the presintered core blanks are placed in a sintering furnace having an oxygen atmosphere and initially sintered at about 920 C. for about 15 minutes. Thereafter, and in the same atmosphere, the core blanks are subjected to an elevated temperature wherein the temperature is slowly and continually raised, for about 10 minutes, to a final sintering temperature of about 1,170 C., and the core blanks are then sintered at this temperature for 10 minutes. The heating is then discontinued and the sintered core blanks are allowed to initially cool in the sintering furnace, containing an oxygen atmosphere, to a temperature of about 920 C., which temperature is generally attained within about 20 minutes. Then the core blanks are removed from the sintering furnace and placed in an oxygen atmosphere at ambient temperatures and allowed to cool to the ambient temperature of about 1 minute.

The above-preferred process may be advantageously modified by presintering the (pulverized) starting mixture of oxides for about 2 hours at about 500 to 800 C. prior to heating in the nitrogen atmosphere. Further, if desired, the relatively rapid cooling of the core blanks to 920 C. from the sintering operation can be replaced by a relatively slower cooling, i.e., from a few minutes to about 10 minutes, in a nitrogen atmosphere.

TABLEl WV, 1,, uV t T, Ferrite in in in in Composition mV mA mV as us A 10.8 1200 82 0.20 0.11

B l0.2 850 87 0.17 0.15 C .7 850 81 0.25 0.12

l, designates the full current, l designates the practical current, 1, designates the rise time, uV designates the peak voltage of the undisturbed or unenergized state of one," wV, designates the peak voltage of the disturbed or energized state of zero, I, designates the switching time and t designates the peak time.

FIG. 2 illustrates, in graphical form, that the temperature dependence of uV wv t and t of a ferrite core composed from composition B (hereinbefore set forth) and manufactured in accordance with the preferred procedure set forth hereinabove. It will be noted that the operating temperature range during which no current readjustment is necessary for this particular ferrite core and for all of the various other ferrite cores produced in accordance with the principles of the invention encompass at least 60.

ln summation, it will be seen that the invention provides an improved ferromagnetic lithium-zinc ferrite data storage core comprising a formed core blank consisting essentially of a sintered mixture of about 3.5 to 15 mol percent ZnO, about 10 to 16 mol percent of U and about 70 to 81 mol percent of Fe O The preferred sintered mixture consists essentially of about 5 to 12.5 mol percent of ZnO, about 12.5 to 15 mol percent of U 0 and 75 to 80 mol percent of Fe O The process comprises forming a core blank from a starting mixture (as set forth hereinabove) and subjecting the formed core blank to a nitrogen atmosphere heated to a temperature of about 880 to 960 C. for a period of time, initially sintering the core blank in an oxygen atmosphere of about 880 to 960 C. for a period of time, finally sintering the core blank in an oxygen atmosphere at a temperature of about 1,060 to 1,220 C. for a period of time, initially cooling the sintered core blank in an oxygen atmosphere to a temperature of about 880 to 960 C. over a period of time and finally cooling the core blank to ambient temperatures in an atmosphere of oxygen or nitrogen over a period of time. The ferrite cores of the invention have a substantially rectangular hysteresis loop exhibiting an R, of greater than 0.7 and having an operating temperature range of at least to 70 C., Le, extending over 60 and exceptionally fast switching times.

It will be understood that modifications and variations may be efiected without departing from the spirit and scope of the novel concepts of the present invention.

1 claim as my invention:

1. A ferromagnetic lithium-zinc ferrite data storage core comprising a formed core blank consisting essentially of a sintered mixture 0f5 to mol percent ofZnO, 12 to 15 mol percent of U 0, and 70 to 81 mol percent of Fe o 2. A ferromagnetic lithium-zinc ferrite data storage core comprising a formed core blank consisting essentially of a sintered mixture of about 5 mol percent of ZnO, about 15 mol percent of U 0 and about 80 mol percent of Fe O 3. A ferromagnetic lithium-zinc ferrite data storage core comprising a formed core blank consisting essentially of a sintered mixture of about 7.7 mol percent of ZnO, about 14.1 mol percent of U 0 and about 78.2 mol percent of P6 0...

4. A ferromagnetic lithium-zinc ferrite data storage core comprising a formed core blank consisting essentially of a sintered mixture of about 12.5 mol percent of ZnO, about 12.5 mol percent of U 0 and about mol percent of Fe O 5. A ferromagnetic lithium-zinc ferrite data storage core comprising a formed sintered core blank consisting essentially of a sintered mixture of about 5 to 15 mol percent of ZnO, about 12 to 15 mol percent of U0, and about 70 to 81 mol percent of Fe O and having a substantially rectangular hysteresis loop with the R being greater than 0.7, said core being operable over a temperature range of 10 to 70 C. without current readjustment.

6. A process of producing a ferromagnetic lithium-zinc ferrite core having a substantially rectangular hysteresis loop consisting essentially of the steps (a) forming a core blank from a presintered starting mixture consisting essentially of about 3.5 to 15 mol percent of ZnO, about 10 to 16 mol percent of U 0, and about 70 to 81 mol percent of mo, and subjecting the formed core blank to a nitrogen atmosphere heated to a temperature in the range of about 880 to 960 C. for about 10 to 30 minutes, (b) initially sintering said formed and heated core blank in an oxygen atmosphere heated to a temperature in the range of about 880 to 960 C. for about 15 to 60 minutes, (0) finally sintering said initially sintered core blank in an oxygen atmosphere heated to a temperature in the range of about 1,060 to 1,220 C. for a period of time ranging from about 10 to 60 minutes, (d) initially cooling said finally sintered core blank in an oxygen atmosphere for about 20 to 30 minutes to a temperature in the range of about 880 to 960 C. and maintaining said temperature for a period of time ranging up to about 60 minutes, and (e) finally cooling said initially cooled core blank in an atmosphere composed of a gas selected from the group consisting essentially of oxygen and nitrogen during a time period of less than about 10 minutes to ambient temperatures.

7. The process as defined in claim 6 wherein (c) the final sintering temperature is attained during a period of time ranging from about 10 to 60 minutes and (d) the initial cooling temperature is attained during a period of time ranging from about 20 to 30 minutes.

8. The process as defined in claim 6 wherein (a) includes pulverizing and presintering the starting mixture for about 2 hours at about 550 to 800 C. prior to forming the core blank. 9. The process as defined in claim 6 wherein (e) comprises finally cooling the initially cooled blank in a nitrogen atmosphere.

10. A process of producing a ferromagnetic lithium-zinc ferrite core having substantially rectangular hysteresis loop and an operating temperature range of about 60 without current readjustment consisting essentially of the steps (a) forming a core blank of a presintered starting mixture consisting essentially of about 3.5 to 15 mol percent of ZnO, about 10 to 16 mol percent of U 0 and about 70 to 81 mol percent of Fe O and subjecting the formed core blank to a nitrogen atmosphere heated to a temperature of about 920 C. for a period of time of about 10 minutes; (b) initially sintering said formed and heated core blank in an oxygen atmosphere at a temperature of about 920 C. for a period of time of about 15 minutes; (c) finally sintering said initially sintered core blank in an oxygen atmosphere at a temperature of about 1,170 C. for about 10 minutes, said temperature being attained during about 10 minutes; (d) initially cooling said finally sintered core blank in an oxygen atmosphere to a temperature of about 920 C., said temperature being attained during about 20 minutes; and (e) finally cooling said initially cooled core blank in an oxygen atmosphere to an ambient temperature within about 1 minute.

11. A process of producing a ferromagnetic lithium-zinc ferrite core having a substantially rectangular hysteresis loop at an operating range of about 60 without current readjustment consisting essentially of the steps of (a) forming a core blank or a presintered starting mixture consisting essentially of about 5 to 12.5 mol percent ZnO, about 12.5 to 15 mol percent U 0 and about 75 to 80 mol percent Fe 0 and subjecting the formed core blank to a nitrogen atmosphere heated to a temperature of about 920 C. for a period of time of about minutes; (b) initially sintering said formed and heated core blank in an oxygen atmosphere at a temperature of about 920 C. for a period of time of about minutes; (c) finally sintering said initially sintered core blank in an oxygen atmosphere at a temperature of about l,170 C. for about 10 minutes, said temperature being attained during about 10 minutes; (d) initially cooling said finally sintered core blank in an oxygen atmosphere to a temperature of about 920 C., said temperature being attained during about minutes; and (e) finally cooling said initially cooled core blank in an oxygen atmosphere to ambient temperatures within about I minute.

12. The process as defined in claim ll wherein the presint ered starting mixture consists essentially of about 5 mol percent of ZnO, about 15 mol percent of U 0 and about 80 mol 

2. A ferromagnetic lithium-zinc ferrite data storage core comprising a formed core blank consisting essentially of a sintered mixture of about 5 mol percent of ZnO, about 15 mol percent of Li2O and about 80 mol percent of Fe2O3.
 3. A ferromagnetic lithium-zinc ferrite data storage core comprising a formed core blank consisting essentially of a sintered mixture of about 7.7 mol percent of ZnO, about 14.1 mol percent of Li2O and about 78.2 mol percent of Fe2O3.
 4. A ferromagnetic lithium-zinc ferrite data storage core comprising a formed core blank consisting essentially of a sintered mixture of about 12.5 mol percent of ZnO, about 12.5 mol percent of Li2O and about 75 mol percent of Fe2O3.
 5. A ferromagnetic lithium-zinc ferrite data storage core comprising a formed sintered core blank consisting essentially of a sintered mixture of about 5 to 15 mol percent of ZnO, about 12 to 15 mol percent of LiO2 and about 70 to 81 mol percent of Fe2O3 and having a substantially rectangular hysteresis loop with the Rs being greater than 0.7, said core being operable over a temperature range of 10* to 70* C. without current readjustment.
 6. A process of producing a ferromagnetic lithium-zinc ferrite core having a substantially rectangular hysteresis loop consisting essentially of the steps (a) forming a core blank from a presintered starting mixture consisting essentially of about 3.5 to 15 mol percent of ZnO, about 10 to 16 mol percent of Li2O, and about 70 to 81 mol percent of Fe2O3 and subjecting the formed core blank to a nitrogen atmosphere heated to a temperature in the range of about 880* to 960* C. for about 10 to 30 minutes, (b) initially sintering said formed and heated core blank in an oxygen atmosphere heated to a temperature in the range of about 880* to 960* C. for about 15 to 60 minutes, (c) finally sintering said initially sintered core blank in an oxygen atmosphere heated to a temperature in the range of about 1,060* to 1,220* C. for a period of time ranging from about 10 to 60 minutes, (d) initially cooling said finally sintered core blank in an oxygen atmosphere for about 20 to 30 minutes to a temperature in the range of about 880* to 960* C. and maintaining said temperature for a period of time ranging up to about 60 minutes, and (e) finally cooling said initially cooled core blank in an atmosphere composed of a gas selected from the group consisting essentially of oxygen and nitrogen during a time period of less than about 10 minutes to ambient temperatures.
 7. The process as defined in claim 6 wherein (c) the final sintering temperature is attained during a period of time ranging from about 10 to 60 minutes and (d) the initial cooling temperature is attained during a period of time ranging from about 20 to 30 minutes.
 8. The process as defined in claim 6 wherein (a) includes pulverizing and presintering the starting mixture for about 2 hours at about 550* to 800* C. prior to forming the core blank.
 9. The process as defined in claim 6 wherein (e) comprises finally cooling the initially cooled core blank in a nitrogen atmosphere.
 10. A process of producing a ferromagnetic lithium-zinc ferrite core having substantially rectangular hysteresis loop and an operating temperature range of about 60* without current readjustment consisting essentially of the steps (a) forming a core blank of a presintered starting mixture consisting essentially of about 3.5 to 15 mol percent of ZnO, about 10 to 16 mol percent of Li2O and about 70 to 81 mol percent of Fe2O3 and subjecting the formed core blank to a nitrogen atmosphere heated to a temperature of about 920* C. for a period of time of about 10 minutes; (b) initially sintering said formed and heated core blank in an oxygen atmosphere at a temperature of about 920* C. for a period of time of about 15 minutes; (c) finally sintering said initially sintered core blank in an oxygen atmosphere at a temperature of about 1,170* C. for about 10 minutes, said temperature being attained during about 10 minutes; (d) initially cooling said finally sintered core blank in an oxygen atmosphere to a temperature of about 920* C., said temperature being attained during about 20 minutes; and (e) finally cooling said initially cooled core blank in an oxygen atmosphere to an ambient temperature within about 1 minute.
 11. A process of producing a ferromagnetic lithium-zinc ferrite core having a substantially rectangular hysteresis loop at an operating range of about 60* without current readjustment consisting essentially of the steps of (a) forming a core blank or a presintered starting mixture consisting essentially of about 5 to 12.5 mol percent ZnO, about 12.5 to 15 mol percEnt Li2O and about 75 to 80 mol percent Fe2O3 and subjecting the formed core blank to a nitrogen atmosphere heated to a temperature of about 920* C. for a period of time of about 10 minutes; (b) initially sintering said formed and heated core blank in an oxygen atmosphere at a temperature of about 920* C. for a period of time of about 15 minutes; (c) finally sintering said initially sintered core blank in an oxygen atmosphere at a temperature of about 1,170* C. for about 10 minutes, said temperature being attained during about 10 minutes; (d) initially cooling said finally sintered core blank in an oxygen atmosphere to a temperature of about 920* C., said temperature being attained during about 20 minutes; and (e) finally cooling said initially cooled core blank in an oxygen atmosphere to ambient temperatures within about 1 minute.
 12. The process as defined in claim 11 wherein the presintered starting mixture consists essentially of about 5 mol percent of ZnO, about 15 mol percent of Li2O and about 80 mol percent of Fe2O3.
 13. The process as defined in claim 11 wherein the starting mixture consists essentially of about 7.7 mol percent of ZnO, about 14.1 mol percent of Li2O and about 78.2 mol percent of Fe2O3.
 14. The process as defined in claim 11 wherein the starting mixture consists essentially of about 12.5 mol percent of ZnO, about 12.5 mol percent of Li2O and about 75 mol percent of Fe2O3. 